This invention relates to a commercial vehicle transmission having an auxiliary box, and more particularly, the invention relates to a configuration of actuators for manipulating the pistons used in shifting the gears of the auxiliary box.
Commercial vehicle transmissions typically include a manual or automated manual main gear box with an auxiliary box connected to the main gear box to provide additional gear ratios. For example, a commercial transmission providing eleven speeds may utilize an auxiliary gear box having three gear planes with two shift forks. Such an arrangement is shown in prior art FIG. 1A. The transmission 10 includes a piston housing 12 having a first 14 and second 16 bores with first 18 and second 20 shift shafts respectively arranged within the bores 14 and 16. Ends of the shift shafts 18 and 20 respectively support first 22 and second 24 pistons. The first 22 and second 24 pistons separate the first 14 and second 16 bores into first 26, second 28, third 30 and fourth 32 chambers. The chambers 26, 28, 30, and 32 are pressurized to move the pistons 22 and 24 from left to right to selectively engage gears within the auxiliary box of the transmission 10.
Pressurized air is selectively provided to the chamber 26, 28, 30 and 32 by four solenoids A, B, C and D. Only one of the chambers for each of the bores is pressurized at any one time to provide a desired gear set. The resultant gear sets for an eleven speed transmission is shown in FIG. 1B. A first gear set including first gear is achieved by pressurizing the second 28 and fourth 32 chambers by turning solenoids B and D on. A second gear set including gears 2 through 6 may be achieved by pressurizing the second 28 and third 30 chambers by turning solenoids B and C on. A third gear set including gears 7–11 may be selected by pressurizing the first 26 and third 30 chambers by turning solenoids A and C on.
The solenoids are rather expensive. Furthermore, the greater number of solenoids used with the transmission 10 the larger the piston housing 12 that is required thereby adding weight and increasing cost. Therefore, what is needed is an improved method and apparatus of achieving a desired gear set while reducing the overall weight and cost of the transmission.